Limb prostheses may operate in response to muscle contractions performed by the user. Some of these prostheses are purely mechanical systems. Other prostheses may incorporate electronic sensors to measure muscle activity and use the measured signals to operate the prosthesis. These types of prostheses may provide only crude control to users that have control over some remaining limb musculature.
Prosthetic devices and other assistive aids that require control over some remaining limb musculature may not be useful for individuals who have suffered from upper spinal cord injury, strokes, and neurodegenerative diseases. Prosthetic devices that operate in response to electrical signals measured by a sensor implanted in the subject's brain are being contemplated for assisting these individuals.